Circuits for the generation of electrical variations



Dec. ,2, 1952 E. l.. c. WHITE 2,620,456 CIRCUlTs FOR THE GENERATION oFELECTRICAL VARIATIONS Filed Feb. 3, 1948 'By -ATTorney Patented Dec. 2,1952 UNTE ST CRCUITS FOR THE GENERATION OF ELECTRICAL VARIATIONS`Application February 3, 1948, Serial No. 6,053 In GreatBrtain February4, 1947 6 Claims;

1 The' present invention relates tol circuits'A for the generation ofelectrical variations and has particular but not exclusive applicationto the' correction of pin-cushion' or: barrel' distor-y tion whichoccursV during scanning of a target electrodein cathode ray tubes used,for example, in television apparatus.`

It is known that to obtain a good focus for all deflection angles of theelectron beam of a cathode-ray tubeof the magnetically deflected type itis necessary to use uniform defiecting aelds. In this case since thelength of the path of an electron in the deecting eld increases withincreasing deviation from the undeiiected path the deection angle of thebeam is not strictly proportional to the current in the deflectingcoils. This tends to cause pin-cushion distortion. Moreover, when as isoften required the electron beam falls on a planek target electrode itis r known that this is'also a factor tending to cause pin-cushiondistortion. Barrel distortion sometimesY occurs as a result of incorrectcurvature of the scanned area with respect to the point about which thebeam is deflected.

Various expedients have heretofore been proposed for correcting suchpin-cushion or barrel distortion but such proposals have usuallyentailed the use of magnetic fields auxiliary to the de'ecting means crthe use of inhomogeneous defi'ecti'ngelds.

Gneof the'objects of thev present invention is to' provide a circuitarrangement embodying a cathode-ray tubehin which either pin-cushion orbarrel distortion is substantially reduced or eliminated in' an improvedmanner.

According toone feature'of the invention there is providedT a circuitarrangement embodying a cathode ray tube, beam defiecting means forscanning the beam of said tube over a target area and means for applyingto said beam deflecting meansscanning waveforms which are such that`eitherv pin-cushion or barrel distortion which would otherwise occur insaid area is substan tially reduced or eliminated.

According to another feature of the invention there'is provided acircuit arrangement embodying a cathode ray tube, beam deecting meansfor scanningV the beam of said tube over a target area and means forapplying to said beam deiiectingk Ymeans scanning waveforms which arelsimilarly modified in accordance with the radial amplitude ofdisplacement of the spot formed byfsaid beam on said target area so thatpin-cushion` or barrelV distortion which would otherwise occur is"substantially reduced oreliminated.v

It will be shown hereinafter that in order to obtain the desiredcorrection for either pincushion or barrel distortion a linear scanningwaveform is required to be modified by a factor (L-ATZ) and accordingvtherefore to a further feature of the invention there is provided acircuit arrangement embodyinga cathoderay tube beamV deflectingVmeans'for scanning the beam ofr said. tube over a target area, means forapply,- ing to said beam deflecting means linear scanning waveformswhich are modified by a factor (1+A1'2) Where r is. the radial amplitudeof di'splacement of the spot formed by said beam on the. target area andAY isa constant so that pincushion. or barrel distortionvwhichWouldother meansv for scanning the beam of said tube at' line and'`frame frequencies, means for integratiing frame frequency oscillations,means for re'-' peatedly interrupting the integration atline fre-`quency and means for applying to said beam defleeting means' line andframeA frequency scanf ning waveforms derived from said integrationprocess so a-s substantially toreduce or eliminate eitherpin-cushion orbarrel distortion which would.' otherwise occur.

According to a further feature of the invention there is-provided'acircuit arrangementembodying a cathode ray tube, beamV` deflecting meansforscanning the beam of said tube at liner and frame frequencies andmeans for applying to said' beam deflecting means'a line frequencydeflecting waveform, said waveform being generated'eby integratingsawtooth variations of line frequency of the form and periodicallyyinterrupting they integration at instants when :r is substantially zeroand then causingk it to recommence from the instantaneous -value thisVterm having the significance hereinafter referred'to.

According to yet av further feature ofthe invention there ist provided acircuit arrangement for the' generation of" electrical variationscomprising a first source of repetitive electrical variations andintegrating means for integrating said variations from said firstsource, a second source of electrical variations and means forinterrupting the integration of the variations from said first sourceand for causing said integration to recommence at a Variable valuedetermined by the variations from said first and second sources.

It can be shown that when a cathode ray beam of a tube falls normallyupon a plane screen in its undeected condition and is deflected on thescreen a distance .r in one of two mutually orthogonal directions, e. g.line deflection, and a distance y in the other of said two directions,e. g. frame deflection under the influence of a homogeneous magneticdeecting field having components I-IT., Hy respectively resolvedparallel with said directions, then the deflections fr, y are relatedvery approximately to the field components He, Hy by the equations:

Where d is the distance of the screen from the point of deflection and kis a factor depending on the charge to mass ratio of an electron and theworking conditions and arrangement of the tube.

It will be seen that deflections x and y are not achieved by componentmagnetic deflecting forces proportional simply to y and :c respectivelybut by these components multiplied by a factor of the form so that r isthe radial amplitude of spot deflection and A is a constant.

Pin-cushion distortion would result if the beam were deflected by forcesproportional to and y but such distortion can be overcome by modifying1the defiecting waveform by the factor l-l-ar2. In the case of barreldistortion the latter can be overcome by modifying the deectingwaveforms by a factor of the same form, the sign of the constant Adetermining the type of correction required.

In order that the said invention may be clearly understood and readilycarried into effect it will now be more fully described with referenceto the accompanying drawings in which:

Figures la), 1(19), 1(c), ltd) and 1(6) are explanatory diagrams,

Figure 2 illustrates a circuit for carrying the invention into effect,

Figure 3 shows a modification of the circuit shown in Figure 2, and

Figure 4 is a block diagram of a circuit arrangement according to afurther form of the invention.

The invention will now be described as applied to the correction ofpin-cushion distortion. In order to generate scanning waveforms inaccordance with Equations 1 and 2 above for defiecting the cathode raybeam of a cathode ray tube at line and frame frequencies, it isnecessary to generate product terms of vmy? and :621/ and to generate an3:3 and g3 term, the act/2 term and the :r3 term being then added to an:c term which is a sawtooth variation at line frequency so as togenerate a corrected line frequency scanning waveform and to add thex21/ term and the yf term to a y term which is a sawtooth variation atframe frequency so as to generate a corrected frame frequency scanningwaveform.

In order to generate the .112g term the product :cy is first generated.In order to generate the product my which is the variation shown inFigure lc, two operations are performed. In Figure 1b of the drawingsthere is illustrated the sawtooth variation y which occurs at framescanning frequency and in the first operation this variation isintegrated by suitable means and the integration is periodicallyinterrupted at line repetition frequency, i. e., at the frequency of theline frequency sawtooth variation and is returned to Zero and theintegration then recommenced so as to generate a variation of the formshown in Figure la. In the second operation, there is added to thevariation shown in Figure la a variation of the form of y, the result ofthe two operations being to produce a variation as shown in Figure 1cwhich is the product term my. In order to generate the term x21/ thevariation .ry is integrated so as to generate the variation shown inFigure 1d and to this variation there is added a variation of the form yso that the required term .1323/ for correcting the frame frequencywaveform is thus generated as illustrated in Figure 1e.

The term ry2 which is required for the line deection correction may begenerated in a manner similar to that described above for the generationof the variation my but in which a variation @l2 is substituted for thevariation y, such Variation y2 being generated by integration of avariation y in known manner.

The Variations 2y and .r1/2 are then added respectively to variations ofthe form of g3 and m3 and variations y and :c so as to generatecorrected waveforms for deflecting the cathode ray beam at frame andline frequencies respectively, the deflection being such thatpin-cushion distortion is substantially reduced so that the beam scans asubstantially rectangular raster.

Figure 2 of the drawings illustrates a circuit for generating thevariations referred to above. In this figure the rectangle Il)represents a source of 'j variations or a source of y2 variations andrectangle 20 indicates a source of repetitive variations at therepetition rate of which the integration process is to be integrated.The variations generated by the source 20 are preferably short durationpotential pulses at line frequency and of negative sense. Valve 30 whichis a valve of the pentode type is so connected that it enables theintegration of the variations generated by source IU to be effected andto be interrupted with the occurrence of each pulse generated by thesource 2G.

Said integration is performed by the valve 3G in known manner. Thusvariations of potential set up at the anode 3l of valve 39 are fed backin negative sense to the -control electrode 32 of the valve through thecoupling capacity 33 so that the circuit presents at the controlelectrode 32 a low impedance for example of the order of the reciprocalof the mutual conductance associated with said control electrode. Thesource l0 is connected with said control electrode through resistanceSi! of magnitude large compared with said low impedance. In thesecircumstances potential variations which are the integral of thevariations of potential difference set up between the output terminalsof source l0 areeestablishedat; the anode 31 ofvalve 301 Thisintegration ls interrupted andi returned to -zero by applyingthe-negative pulse of ipotentiall gen` erated byfsource '2B- to thesuppressor electrode of I valve` 30'2 so. asA toa-renderA said Valve znon:- conducting with-the arrival ofeach of v saidpulses.y Thevariations set `upatv .the-:anode 3 Ifof"valvc 3D1 or theirinverted-replica set `up atthe cathode 3% of'valVeare applied -to mixingmeansor-'mixingfwith the variations-fromA source |03 so thattherequiredvariations are inally-A set up: The circuit shown in Figure2canthus1beemployed' togenerate a' variation of'form y'andv inthecasewherethecircuit is usedl for generating a correcting term forframe frequency deflection tl'ie`outputfrom\ the' mixing means 375 isapplied ton aV further-'integrator 38- to which is also fedVer'yariation` of the` form yr so that*thefterml mZ'y isset-up; Where thecirc-uit shownin Figure 2 is employedi for generating'the my? term; thenthe source; l B is arranged toY generate variations ofthe' form' y.2`and the: further: integratori-58v is omitted.

The variations :1:3 and 2/3 are` generated' by twiceV integratingvariations'of. the formes: and

in known. manner. and these, variations; to,- gether with variations ofthe forms andy are then added to the Variations` m12 and'x2y to producecorrecteddeectingwaveforms according to Equations 1 and 2`above.

In a modified form of circuit the variations Whose integration., is tobe'interrupted are app lied througliaeresistance to a capacity which.becomes lcharged to. a degreeA suiciently accu-Y rately representativeof the integral'jof 'said1vari--- ations and said capacity isperiodically discharged by bi-directionally switching means whichinterrupts the integration and. returns it to zero under. thecontrol of.repetition .pulsesso thatrequired variations are generated.

Figure 3. illustrates by way ofA examplesuch a modified formof circuit.The Variations: of po.- tential to be, integratedy i. e., from sourceI8.` referredtoaboveare applied to terminal'50 and resistance Eil and`capacity.A 52. constitute a well. knownform of integratngcircuit.. l'nthisfcir-A Cuitthe integral .ofthe applied variations appearsasadi'erence of potential between the.- plates ofcapacityf52.TheAdouble-diode. valve 60-is abi directional switching device for.discharging cai-A pacity-52 substantiallyto zero irrespective-:--ofVits: senseof charge. Said double-diode. valvefis con-r trolled by therepetition pulses from. sourcev 2d` referred to above which are appliedto the control-electrode 'H o'fevalvev'l.l This-Valvefis connected torepeat said pulses at its cathode 12 and to repeat said pulses invertedat its anode 13. The repeatedpulses of both senses are appliedrespectively to the anodel and cathode 'I5 of the double-diode valveSSI-throughthe'-coupling condenserslandl'leand resistances 18 and 19.Thus, Whatever is the sense ofv charge of capacity 52 the incidenceoiany of said repeti tivepulsesat electrodey 'H- of` valve 'Ff causes thedischarge-of capacity 52substantiall'yftozero thusV interrupting theintegration and causing it to recommence from substantially zero.The'output fromth-e condenser- 52 is tlien modiedv inthe-mannendescribed with reference to -Figure\2.

A. modificationn of` the invention will nowA be described. It followsfromA equation (1') by differentiation with respect to timew thatparedjwithD. Inzthis case;EquationBE-may:bec

reduced/tos Deden): 1 ggg- 25%) yDe Since: the scanning.; action. intelevision: isfy conn monlyr required to. be carried out'. atuniformwelocityg; thatv is to.. say such'. that'. Dx is, constant.-it'followsthat the line deflection of suchxscarr.-A ning maybeperformed.. corrected? for' instance' for: pin-cushion: distortionbymeans arranged` to*A effect: integration'. of" a varationzof" the`form:

2d? Zd A-.variation of. the: last-mentioned formt is: pro;- duce dzbyad-dingV insuitableproportionsivariationss of'theform` 3:2 and :u2together with aconstant.- Theecombinationzisthenintegratedandheiintegration-is arrangedrtdbe interrupted. atv instantswhen.A is'- a. maximum; and" thei integration is then cause diV to: beabrought'- to.` the l correct' starting-1-y valuefof.

112; QL-2612' 221.2k

' whereV x0 is the minimum value of TfhefW-ave formvrequiredfor'deecting the beamat. frame frequency canfbe .generated .by the.arrangementsy describedwith referencefto,Figurev 2.011. 33.`

Eigureeti of.A the drawings, illustrates in blocki form a'circuitxsuitablefor use1in this-modified formi the invention. As shown in thisgure,` therectangle represents a-source of` repetitive. pulses.occurring at line-*frequencywhichl are fedA toan integrator 8| whichserves to generate sawtooth-variations of the formar; referred torabove.Thesesawtooth variations are fedto a further integrator 82` which servesto `generate.-Variations:v of the form` fr?. Theoutput fromthee-integrator.` 82, is-applicd to -an additive combining? circuit' 83fwhich is fed with variations 2'.V l-z..

from .ae source. Theoutput from-theacombinz-,k ing. circuit 33. isI fed.toanintegraton 85. and thev outputAfror-nthe integrator 854 is ,fed toan-inter-- rupter 85. The ,integraton 85 and the'V interrupten 8.8i are`controlled by pulses from the-i. source 80': at instants .when :1: is atits maximum. valuefsoy that the integrated output from theintegratoivBtl is :caused `tov-recommence- -from, alva'lue which is -adjustedetothe instantaneousfvaluei y2. x0 (l 2032 2012 whichissuppliedffromasource8'1v fed from the:` source.

Theepurpose of:A the interrupter 86is,.toensure: that the integration.always commences.y attthe. correct instantaneous value at the commencement of each line. For this purpose the interrupter 86 will include abifdirectionally conduct-l lng switch such" as is disclosed in BritishPatent No. 512,109 so thatafterY the integration process is interruptedthezzlevel from which it recommences is determined from the variationsgenerated by the source 81. There is thus set up in the output of theinterrupter 86 an output which corresponds to the integral of l y2 3x22df'2d2 which is the required line scanning waveform.

Although the invention has been described above as applied to thecorrection of pin-cushion distortion it will be appreciated that barreldistortion can be similarly corrected, the scanning waveforms requiredfor correcting such barrel distortion being obtained merely by changingthe signs of some of the terms referred to above.

Although the invention is mainly applicable for use in cathode ray tubesin which the beam is deflected by electromagnetic means, it will beunderstood that the invention is equally applicable to the generation ofscanning waveforms suitable for use in the electrostatic deflection ofcathode ray beams.

I claim:

1. A circuit arrangement embodying a cathode ray tube having a targetarea which if scanned in a uniform linear manner would exhibit eitherpin-cushion or barrel distortion, beam deflecting means for scanning thebeam of said tube over said target area, means for generating scanningwaveforms, means for modifying said waveforms in accordance with theradial amplitude of displacement of the spot formed by said beam on saidtarget area, and means for applying said modified waveforms to said beamdeecting means to substantially reduce pin-cushion or barrel distortion.

2. A circuit arrangement embodying a cathode ray tube having a targetarea which if scanned in a uniform linear manner would exhibit eitherpin-cushion or barrel distortion, beam deecting means for scanning thebeam of said tube over said target area, means for generating linearscanning waveforms at line and frame frequencies, and means formodifying said waveforms by a factor (1+A'r2) where r is the radialamplitude of displacement of the spot formed by said beam on the targetarea and A is a constant, and means for applying said modified waveformsto said beam deflecting means, whereby pin-cushion or barrel distortionin said area is substantialls7 reduced or eliminated.

3. A circuit arrangement embodying a cathode ray tube having a targetarea which if scanned in a uniform linear manner would exhibit eitherpin-cushion or barrel distortion, beam deflecting means for scanning thebeam of said tube over said area at line and frame frequencies, meansfor integrating frame frequency sawtooth oscillations, means forrepeatedly interrupting the integration at line frequency, and means forapplying to said beam deflecting means line and frame frequency scanningwaveforms derived from said integration process substantially to reduceor eliminate either pin-cushion or barrel distortion.

4. A circuit arrangement embodying a cathode ray tube, beam deiiectingmeans for scanning the beam of said tube at line and frame frequencies,means for applying to said beam deflecting means waveforms in accordancewith the forwherein lc is a factor depending on the charge to mass ratioof an electron, and y are deflection distances in two mutuallyorthogonal directions of the beam on the'tube screen under the influenceof a homogeneous magnetic eld having components Hx and Hy respectivelyresolved parallel with said directions, and dis the distance of the tubescreen from the point of deiiection of the beam, said means for applyingthe waveforms including means for integrating a variation y2 andperiodically interrupting said integration at the repetition frequencyof the variation and means for adding thereto a variation of the form y2to generate a term :c1/2, further means for integrating a sawtoothvariation y, means for periodically interrupting said latter integrationat the repetition frequency of the variation zr, means for addingthereto a variation of the form y to generate a product term xy, andmeans for integrating the variation .ry and adding thereto a variationof the form y to generate the term :32g and finally means for addingsaid variations :r1/2 and m22/ to variations of the form .r3 and g3 andto variations of form J: and y.

5. A circuit arrangement embodying a cathode ray tube, beam deiiectingmeans for scanning the beam of said tube at line, and frame frequenciesand means for applying to said beam deflecting means a line frequencydeflecting waveform, and means for generating said waveform includingmeans for integrating sawtooth variations of line frequency of the form11:, means for periodically interrupting the integration at instantswhen is substantially a maximum, and means for restarting theintegration from the instantaneous value y2 x03 x 1 2d2 2d2 wherein xois the minimum value of .r and :I: and y are deection distances in twomutually orthogonal directions of the beam on the tube screen. and d isthe distance of the tube screen from the point of deection of the beam.

6. A circuit arrangement for the generation of electrical variations,comprising a first source of repetitive electrical variations andintegrating means for integrating said variations from said firstsource, a second source of electrical variations, and means forinterrupting the integration of the variations from said first sourceand for restarting said integration at a variable value determined bythe variations from said first and second sources. e

ERIC LAWRENCE CASLING WHITE.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 2,183,340 Tolson Dec. 12, 19392,224,005 Vance Dec. 3, 1940 2,237,651 Bruche Apr. 8, 1941 2,305,930Martinelli Dec. 22, :1942 2,313,971 Roe Mar. 16, 1943 2,449,524 Witherbyet al. Sept. 14, 1948 2,463,969 Hulst, Jr. Mar. 8, 1949 2,464,393 HeimMar. 15, 1949 2,467,834 Lasher, Jr. Apr. 19, 1949 2,485,594 HallmarkOct. 25, 1949 2,574,946 White Nov. 13, 1951

